1. Field of the Invention
The present invention relates to article storage facilities having a article storage rack and moving members such as stacker cranes for transporting articles between the article storage rack and article supports for articles transported in and out.
2. Description of Related Art
In such article storage facilities, it is required to improve the transport ability in order to shorten the time for storing and retrieving articles.
Thus, examples of conventional article storage facilities include a facility that is provided with a vertically movable unit that can be vertically moved with respect to an article-transporting moving member, wherein two article transfer means are aligned in the horizontal direction on the vertically movable unit (see JP 2000-229708A, for example).
In this first known structure, it is possible to transfer an article with each of the two article transfer means by horizontally moving the article-transporting moving member and by vertically moving the vertically movable unit, and thus it is possible to transport two articles at the same time with one article-transporting moving member, so that the transport efficiency can be improved.
Furthermore, in another conventional article storage facility, two article-transporting moving members are provided in such a manner that they horizontally move on the same track, two support portions for articles transported in and out are provided in such a manner that they are installed on both sides of an article storage rack, one article-transporting moving member among the two article-transporting moving members transports an article between one support portion for articles transported in and out and the article storage rack, and the other article-transporting moving member transports an article between the other support portion for articles transported in and out and the article storage rack (see JP 2002-175117A, for example).
In this second known structure, in the horizontal direction, a common area is provided at the middle portion of the article storage rack, and individual areas are provided on both ends of the common area. Either one of the two article-transporting moving members can enter the common area, but a restriction is performed such that the two article-transporting moving members do not enter the common area at the same time, and thus the article-transporting moving members are prevented from colliding against each other. In the two individual areas, the article-transporting moving members can transport articles at the same time, and thus the transport ability can be improved.
In the first known structure, the two pieces of article transfer means are aligned in the horizontal direction on the vertically movable unit. Thus, if a command to transport two articles to different storage portions among a plurality of storage portions in the article storage rack is given, or if a command to transport two articles from different storage portions among the plurality of storage portions in the article storage rack is given, then the articles are one by one transferred to and from the different storage portions.
More specifically, in a case where two articles are transported to different storage portions, when transferring the two articles to be stored in the different storage portions, first, one piece of article transfer means among the two pieces of article transfer means is positioned at an article transfer position on the rack side corresponding to the storage portion in which an article is to be stored, and the article is taken in by transferring it so as to be stored in the storage portion. Next, the other article transfer means is positioned at an article transfer position on the rack side corresponding to the storage portion in which the other article is to be stored, and the remaining one article is taken in by transferring it so as to be stored in the storage portion.
Accordingly, although two pieces of article transfer means are provided on one article-transporting moving member, the transport ability of only one piece of article transfer means can be obtained for transfer to and from the storage portions, and therefore there is the possibility that the transport ability cannot be effectively improved.
In the second known structure, although two article-transporting moving members are provided, the two article-transporting moving members cannot enter the common area of the article storage rack at the same time, and thus the two article-transporting moving members cannot transport articles at the same time in the common area. Accordingly, the transport ability of only one article-transporting moving member can be obtained for article transportation to and from a part of the article storage rack in the common area, and therefore there is the possibility that the transport ability cannot be effectively improved.